The invention involves a device for the relative rotation of a camshaft relative to a crankshaft that drives the camshaft in an internal combustion engine, in which the device is attached on a drive-side end of the camshaft and projects into a chain bay of a cylinder head of the engine. The device includes a hydraulic adjusting drive with a structural component that is adapted to be drivingly connected with the crankshaft of the internal combustion engine and a second structural component adapted to be connected to the camshaft in a rotationally fixed manner. The structural component which is adapted to be drivingly connected to the crankshaft is in force-transferring connection with the second structural component that is affixed to the camshaft, and can be acted upon alternatingly or simultaneously by a hydraulic pressure agent via two pressure chambers located within the device such that the structural parts can be rotated or fixed in position relative to each other. The pressure agent supply and return to and from the pressure chambers are controlled by a hydraulic control component arranged coaxially to a longitudinal axis of the camshaft in a cavity of an axial structural component of the device. The hydraulic control element is activatable through an adjusting element attached to an opposing housing part of the chain bay in a position aligned with an extension of the camshaft longitudinal axis as a function of the operating parameters of the internal combustion engine.
A device of this type that forms the generic concept is previously known from German Patent DE-OS 196 11 365. This device, essentially constructed as a hydraulic adjustment mechanism, is arranged on the drive-side end of the camshaft which projects into a chain bay of the cylinder head of the internal combustion engine and consists of a structural component affixed to the crankshaft that is driven in connection with the crankshaft of the internal combustion engine and a structural component that it is rotationally fixed to the camshaft. The structural component affixed to the crankshaft is in force-transferring connection with the structural component that is fixed to the camshaft, where both of them are constructed with helical gearing into which an adjustment piston meshes. The adjustment piston has complementary helical gearing and is arranged inside the device and can be moved axially. Through the use of two pressure chambers that are constructed within the device and can be acted upon alternatingly or simultaneously with a hydraulic pressure agent, and which are separated from each other by the adjustment piston, both structural parts can then be rotated or fixed and cause a relative rotation or an infinitely variable hydraulic fixing of the camshaft relative to the crankshaft. The pressure agent supply and return to and from the pressure chambers of the device can in addition be controlled by a hydraulic control component arranged coaxially to the camshaft longitudinal axis in a cavity of an axial structural component of the device, where the axial structural component is constructed as a mounting bolt, having a hollow shaft part, for the structural component affixed to the camshaft, and can be screwed into a threaded bore hole arranged coaxially to the camshaft longitudinal axis. The hydraulic control element is formed from an axially movable control piston that is arranged in the hollow shaft part of the mounting bolt and rotates together with the device and is connected to an adjusting element via a tappet push rod. This adjusting element that is activated as a function of the operating parameters of the internal combustion engine is attached to a housing part of the chain bay lying opposite in the extension of the camshaft longitudinal axis, and is constructed as an electromagnet that acts against the force of a restoring spring.
It is disadvantageous in this known device that its hydraulic control element and its adjusting element or its electromagnet and its armature that is connected to the control piston, are attached or positioned on two different structural parts of the internal combustion engine, namely on the one hand, on the fixed chain bay housing and on the other hand, on the rotating cam shaft end, and thus are subject to many perturbation factors which can negatively affect the accurate combined interaction of these elements, which is necessary for the functioning of the device, or are the cause of internal pressure agent leakages or malfunctions of the device. Thus, for example, because of the, for the most part, very coarse position tolerances both in the radial as well as in the axial directions, between the chain bay housing and the camshaft ends, it is only possible by relatively expensive centering measures, to mount the electromagnets with the necessary accurate axial and radial air gaps on this armature in the chain bay housing. On the other hand, in spite of axially accurate positioning of the electromagnets relative to this armature, it is unavoidable that by perturbation factors acting in the radial direction during the operation of the internal combustion engine, such as for example, by the camshaft-bearing play and/or by a deflection of the camshaft end and/or the tension of the drive chain, the radial air gap of the armature to the electromagnets becomes asymmetrical so that the armature is more strongly magnetically attracted on one side and at least makes control of the regulated positions of the control pistons more difficult, or in the worst case, becomes impossible by unbalancing or clamping of the control piston. In addition, the perturbation factors acting in the axial direction during the operation of the internal combustion engine, such as for example, the axial vibrations of the camshaft which come from the valve operations of the internal combustion engine, or the temperature-dependent expansions of the chain bay housing and the camshaft, negatively influence the force equilibrium between the electromagnets and the restoring spring of the control piston acting against them, or the hysteresis and the response sensitivity of the electromagnets, so that an exact control of the hydraulic resistances or the pressure agent inflow and outflow to and from the pressure chambers of the device is only possible by a corresponding overdimensioning of the electromagnets. This overdimensioning of the electromagnets has, however, proven in view of the increased manufacturing costs for a device of this type, to be disadvantageous, and can also not completely eliminate the disadvantageous effects resulting from the axial and radial interference factors, so that internal pressure agent leakages and/or hydraulic leakages between the pressure chambers of a device of this type can not be further ruled out.